Liquid seal

ABSTRACT

A non-contacting seal which includes a stationary tooth that radially overlaps a tooth on a rotatable shaft, with the sealing action resulting from controlled clearance both radially between stationary tooth and the shaft, and axially between the stationary tooth and the shaft. The seal may also be in the form of a stationary tooth that is approximately in the same radial plane as a tooth on a rotatable shaft, with the sealing action resulting from both a controlled clearance gap between the two teeth and from the momentum of liquid traveling outward from the rotating tooth making it difficult for the liquid to turn to go axially through the gap between the rotating tooth and the stationary tooth. The seal may also comprise the combination of the two seals described above or a pair of the same seals, i.e., two radially overlapping or two in the same radial plane.

BACKGROUND OF THE INVENTION

[0001] This invention relates in general to a seal and more specificallyto a non-contacting device that prevents a liquid such as oil fromescaping from an enclosed cavity such as a gearbox along a rotatableshaft.

[0002] Gearboxes typically use oil as a lubricant both between the gearteeth and in the bearings that support the shaft. The level of the oilis below the opening for the shaft, but typically when operating thegearbox is filled with a mist of oil. Oil is also splashed throughoutthe gearbox either by the action of the gear dipping into the oil or bya pressurized lubrication system that supplies oil to the bearings andsprays oil onto the gears. Leakage of this oil can cause environmentaland economic problems. For example, in many high-speed centrifugalcompressors the impeller is mounted directly on the output shaft of thegearbox. When the compressor is unloaded any oil that gets out of thegearbox may get sucked into the compressor and contaminate what shouldbe an oil free area. When the compressor is subsequently loaded, the oilcan travel with the compressed gas and contaminate the process. This isunacceptable in many plants, such as in pharmaceutical manufacturing.

[0003] One type of seal used extensively to prevent oil leakage from agearbox is the mechanical seal. This type of seal, however, is speedlimited and therefore cannot be used for very high speed shafts such asthose used in centrifugal compressors. This is because typicalmechanical seals generate excessive heat due to the mechanical shearingof the oil at high peripheral speeds. Mechanical seals may also wearover time, and need periodic replacement.

[0004] Another seal type that is well known in the art is the labyrinthseal. Since this type of seal is non-contacting, it is used extensivelyon high-speed equipment. Unfortunately, they are not very good oil sealsunless either a buffer gas is used to assure that there is a continuousflow of gas towards the gearbox to prevent the oil from migrating out orenough axial space is provided for at least two sets of teeth with anoil drain between them. Use of a buffer gas adds to both initial,ongoing and maintenance costs, while lowering reliability. Addingadditional axial space may cause rotodynamic problems, as well as addedcost to the system.

[0005] As can be seen from the above description, oil seals in the pasthave worked with varying degrees of efficiency, but have either requiredexternal support, lacked reliability or required a large axial space.

SUMMARY OF THE INVENTION

[0006] It is therefore an object of the present invention to provide aseal means which overcomes the problems of the prior art describedabove.

[0007] It is another object of the present invention to provide a sealwhich prevents oil leakage from an enclosure along a rotatable shaft.

[0008] It is a further object of the invention to provide a simple sealdesign that does not rely on external support for its proper operation.

[0009] Another object of the present invention is to provide a sealdesign which minimizes the axial length needed for the oil seal.

[0010] These and other objects of the present invention are obtained bythe configuration of a rotatable shaft operating in conjunction withstationary seal teeth connected to a housing or suitable support.

[0011] The present invention is directed to an annular non-contactingseal comprising a stationary tooth that radially overlaps a tooth on arotatable shaft, with the sealing action resulting from controlledclearance both radially between the stationary tooth and the shaft andaxially between the stationary tooth and the shaft. In a secondembodiment the non-contacting seal may comprise a stationary tooth thatis approximately in the same radial plane as a tooth on a rotatableshaft, with the sealing action resulting from both the controlledclearance between the two teeth and from the momentum of the liquidtraveling outward from the rotating tooth making it difficult for theliquid to turn to go axially through the gap between the rotating toothand the stationary tooth. In a preferred embodiment, the seal maycomprise the combination of the seals in the two embodiments describedabove. The stationary teeth which comprise the seal may be made of anysuitable material. Typical materials include metals, plastics andceramics. In one embodiment the seals were made of an aluminum alloy.

[0012] The seal functions to prevent oil leakage from an enclosureadjacent or surrounding a rotatable shaft such as that used in a highspeed centrifugal compressor in which an impeller is mounted on theoutput shaft of a gearbox.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For a fuller understanding of the nature and objects of theinvention, reference should be made to the following detaileddescription of a preferred mode of practicing the invention, read inconnection with the accompanying drawings, in which:

[0014]FIG. 1 is a schematic plane view of one embodiment of the sealshowing its proximity to a bearing.

[0015]FIG. 2 is a plane view of a second embodiment of the seal alsoshowing its proximity to a bearing.

[0016]FIG. 3 is a sectional plane view of part of a centrifugalcompressor (or turbine) stage utilizing the seal system of the presentinvention.

[0017]FIG. 4 is a schematic plane view of a third embodiment of theseal, designed with identical teeth.

[0018]FIG. 5 is a schematic plane view of a fourth embodiment of theseal that allows assembly without splitting the stationary part of theseal.

[0019]FIG. 6 is a schematic plane view of a fifth embodiment of theseal.

DETAILED DESCRIPTION OF THE INVENTION

[0020] For a better understanding of these and other objects of thepresent invention, reference shall be made to the following detaileddescription of the invention, which is to be read in association withthe accompanying drawings.

[0021]FIG. 1 is a schematic representation of one embodiment of thepresent invention. In FIG. 1 a shaft 10 typically has two oil slingers12 and 16 respectively, and each oil slinger has a stationary toothassociated with it. The bearing side stationary tooth 14 (towards theinside of the enclosure or housing 20) is in close proximity to theoutside diameter of oil slinger 12. This tooth and slinger combinationlimits the amount of oil that can reach the groove or cavity 13 betweenthe two slingers. Groove 13 should be sufficiently large that any liquidthat leaks into it flows down the groove without filling it, and doesnot bridge the groove due to capillary action. Furthermore, when shaft10 is rotating, oil on the shaft will be thrown from the rotatingslinger tooth 12 and its momentum will carry it past the gap 15 betweenrotating slinger tooth 12 and the stationary tooth 14. The high velocityflow of liquid past the gap may act as a venturi, and actively draw airinto the gearbox, thus preventing leakage of oil out. Any oil that doesget past this first slinger is channeled around the shaft either in thegroove 13 between the two oil slingers or in the gap 17 between the twoteeth 14 and 18. The oil is then drained back into either the gearbox orthe oil reservoir (not shown). The primary tooth 18 is designed tooverlap the primary oil slinger 16 in the radial direction, i.e. the tipdiameter of the tooth is just slightly larger than the root diameter ofthe oil slinger. Both the radial gap 19 from the shaft to the primarytooth and the axial gap 21 from the primary tooth to the primary slingermust be controlled, but this is not difficult to do with normalmanufacturing tolerances. For a shaft having a diameter of about 1½inches, gaps 15 and 19 are in the range of about 0.004-0.010 inches,with axial gap 21 being in the range of about 0.005-0.045 inches.

[0022] Oil that gets into the axial gap 21 between the tooth and oilslinger will not go through the small gap 19 between the tooth and theshaft when the shaft is stationary, and is thrown out of the axial gapby centrifugal force when the shaft is rotating. Even droplets of oil onthe face of the tooth that are so small that they do not bridge the gapwill be moved outward by centrifugal force due to the rotation of theair in the gap between the tooth and slinger. Thus oil or other liquidwill be retained in the gearbox or similar enclosure whether or not theshaft is rotating.

[0023] It is possible to use either tooth and slinger pair combinationseparately, but the preferred embodiment of this invention uses the twopair together. FIG. 1 illustrates a sloped outer side 14A on thesecondary seal tooth so liquid thrown from the rotating slinger toothwill be deflected. FIG. 2 illustrates a straight outer side 14B on thesecondary seal tooth so a split bearing (not shown) that is in veryclose proximity to the rotating slinger tooth may be removed radiallywithout disturbing the stationary seal tooth. Note that the face 12A ofthe slinger tooth 12 may also be used as a thrust surface that thebearing acts upon (in either the configuration illustrated in FIG. 1 orFIG. 2).

[0024]FIG. 4 is a schematic plane view of a third embodiment of thepresent invention. In FIG. 4 the two stationary teeth 18 and 28 aresubstantially similar, and the two oil slingers (rotating teeth) 16 and26 are substantially similar. In this configuration, the stationaryteeth must normally be split to allow assembly. Groove or cavity 13 isagain provided to direct any oil that does get past tooth 28 and slinger26 down to the bottom of gap 17 (FIG. 3) where it will be drained.

[0025]FIG. 5 is a schematic plane view of a fourth embodiment of thepresent invention. In FIG. 5 the two stationary teeth 18 and 28 aresimilar, however tooth 28 is displaced radially outward so that theinner diameter of tooth 28 is greater than the outer diameter of tooth16, thus allowing axial assembly of the teeth over the slingers. Agroove or cavity 13 is provided to direct any oil that does get pasttooth 28 and slinger 26 down to the bottom of gap 17 where it will bedrained.

[0026]FIG. 6 is a schematic plane view of a fifth embodiment of thepresent invention. In FIG. 6 the two stationary teeth 14 and 24 aresimilar, though they may be mirror images. Assembly of thisconfiguration is simple because there is no radial overlap. Slinger 12and stationary tooth 14 may be configured the same way as was describedfor FIGS. 1 or 2. Tooth 24 acts as a normal labyrinth tooth, except itacts in conjunction with the outer diameter of slinger tooth 22 ratherthan with a shaft surface. A groove or cavity 13 is provided to directany oil that does get past tooth 14 and slinger 12 down to the bottom ofgap 17 where it will be drained.

[0027]FIG. 3 is a plane view of part of a centrifugal compressor 30 (orturbine) stage utilizing the seal system of the present invention.Reference character 32 illustrates the compressor (or turbine) impellerwhich discharges air or other gas at area 34. The shaft 10 transmitspower to or from the impeller. The shaft 10 is rotationally symmetric.The shaft is supported on radial bearing 36, and may also be supportedby another bearing (not shown). The bearing may be designed to also actas a thrust bearing, and could use the bearing side slinger face 12A asa thrust surface.

[0028] A seal 38 is designed to restrict the flow of air or other gasbetween from behind the impeller (area 40) to the cavity 42. Cavity 42is freely vented to atmosphere, so the pressure in cavity 42 should beatmospheric. However, when the pressure in area 34 and therefore thepressure in area 40 is below atmospheric, the leakage of gas from 42 to40 may cause cavity 42 to be very slightly below atmospheric.

[0029] The flow of oil from the pressurized radial bearing 36 mayforcefully impinge on the face 12A of bearing side slinger 12 where itwill be turned to either flow radially outward away from the shaftand/or to move tangentially around the shaft and drip off slinger 12.Bearing side seal tooth 14 is in very close radial proximity to slinger12, so little if any oil will leak through the very small gap betweenthem. Any oil that does get through the gap between bearing side sealtooth 14 and slinger 12 will either be caught in groove 13 and flow tothe bottom of the shaft where it will drip off or it will just flowalong the walls of cavity 17 to the bottom, where it will flow throughdrain 46 back into the gearbox, and then down drain 48. Drain 46 may bejust a hole or slot in the bearing side seal tooth 14 as shown, or itmay be a drain with a liquid trap to prevent the communication of gasesbetween cavity 17 and the gearbox drain 48.

[0030] The impeller side tooth 18 overlaps slinger 16 as shown in FIGS.1, 2, 3, 4 and 5. It is both in close radial proximity to the shaft 10and in close axial proximity to slinger 16. The slingers 12 and 16 maybe integral with or shrunk onto the shaft 10.

[0031] Drain 50 may be provided to drain any oil that does get past theseals, and may also serve as the vent for cavity 42.

[0032] While the present invention has been particularly shown anddescribed with reference to the preferred mode as illustrated in thedrawing, it will be understood by one skilled in the art that variouschanges in detail may be effected therein without departing from thespirit and scope of the invention as defined by the claims.

I claim:
 1. A non-contacting annular seal for a rotatable shaft withsaid shaft having an axis of rotation in a substantially horizontalplane which comprises in combination: (a) first seal means whichincludes a first stationary tooth that radially overlaps a first toothon a rotatable shaft, with the sealing action resulting from controlledclearance both radially between the stationary tooth and the shaft andaxially between the stationary tooth and the shaft; (b) second sealmeans adjacent said first means which includes a second stationary tooththat radially overlaps a second tooth on a rotatable shaft, with thesealing action resulting from controlled clearance both radially betweenthe second stationary tooth and the shaft and axially between the secondstationary tooth and the shaft; (c) first drain means positioned betweenthe said teeth on said rotatable shaft comprising a groove between saidteeth, which functions to enhance the sealing action by guiding anyliquid around the shaft to the bottom rather than allowing unimpededflow axially along said shaft; (d) second drain means positioned betweenthe said stationary teeth comprising an annular cavity which functionsto guide liquid away from the radial gap between said rotating andstationary teeth; and (e) third drain means positioned through thebottom of said second stationary tooth means which functions to allowany liquid between two said seal means to flow back to a gearbox orreservoir.
 2. The seal of claim 1 in which the second stationary toothis displaced radially outward so that the inner diameter of said secondstationary tooth is greater than the outer diameter of said first toothon said rotatable shaft.
 3. A non-contacting annular seal for arotatable shaft with said shaft having an axis of rotation in asubstantially horizontal plane which comprises in combination: (a) firstseal means which includes a first stationary tooth that is approximatelyin the same radial plate as a first tooth on a rotatable shaft, with thesealing action resulting from both a controlled clearance gap betweensaid two teeth and from the momentum of the liquid traveling outwardfrom said rotating tooth; (b) second seal means adjacent said firstmeans which includes a second stationary tooth that is approximately inthe same radial plane as a second tooth on a rotatable shaft, with thesealing action resulting from both a controlled clearance gap betweensaid two teeth, and from the momentum of the liquid traveling outwardfrom said rotating tooth; (c) first drain means positioned between thesaid teeth on said rotatable shaft comprising a groove between saidteeth, which functions to enhance the sealing action by guiding anyliquid around the shaft to the bottom rather than allowing unimpededflow axially along said shaft; (d) second drain means positioned betweenthe said stationary teeth comprising an annular cavity which functionsto guide liquid away from the radial gap between said rotating andstationary teeth; and (e) third drain means positioned through thebottom of said second stationary tooth means which functions to allowany liquid between two said seal means to flow back to a gearbox orreservoir.